This invention relates to methods and apparatus for detecting missing, misaligned or mislocated parts in machine assemblies. More specifically, this invention relates to a method and apparatus for detecting missing bearings in an engine assembly.
The assembly of a multicylinder internal combustion engine is a very complicated process requiring precise coordination between a plurality of humans and a plurality of machines, each employed at various stages in the process of forming the engine assembly. Whereas much progress has been made in the area of quality control with respect to engine assembly, it is still not uncommon for an engine to be assembled with one or more parts missing or misplaced. Specifically, as an engine is assembled, a bearing insert or shell is manually inserted into the bearing housing at the crankshaft end of the connecting rod. The connecting rod is then positioned against the respective pin on the crankshaft, the other bearing insert or shell half is manually inserted into the bearing cap, and the bearing cap with insert is positioned over the exposed half of the crankshaft pin and buttoned down to the connecting rod to complete the bearing assembly between the connecting rod and the crankshaft. On occassion, an operator either fails to insert one or both of the inserts or the insert is inserted but becomes misplaced before final assembly of the bearing is accomplished. In either case, the completed engine is missing one or both of the bearing inserts and will soon destroy itself in actual operation.
Various methods and apparatus have been proposed to detect missing bearings in the completed engine assembly. In the most commonly used technique, the engine is substantially totally assembled, at least to the point where the lubricating passages within the engine are complete; oil is supplied to the engine, the engine is spun; and the oil pressure is monitored to detect a drop in pressure corresponding to a missing bearing insert in a particular piston subassembly. Whereas this system is generally effective, it occurs at such a late stage in the assembly process that correction of the detected problem requires essentially complete disassembly of an essentially completed engine. It has also been proposed to pump air through the oil passages and monitor the air pressure to detect a missing bearing insert but this procedure can also be performed only at such time as the engine has been completed to the point of establishing the oil passages and therefore also entails essentially complete disassembly of an essentially completed engine in situations where a missing bearing insert is detected. Both of these prior art techniques also are rather time consuming and involve rather complex support apparatus, in the one case to supply pressurized oil to the engine assembly and in the other case to provide pressurized air to the engine assembly.